1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements such as nails, bolts, pins and the like in a constructional component and including at least one combustion chamber for receiving an oxidant-fuel gas mixture, a piston guide located adjacent to the combustion chamber and in which a drive piston for driving the fastening elements in is displaceable by combustion gases produced by combustion of the oxidant-fuel gas mixture in the combustion chamber, and ventilator means for producing turbulence in the combustion chamber and including a ventilator drive.
2. Description of the Prior Art
Setting tools of the type described above can be driven with gaseous or evaporated liquid fuels that are combusted in the combustion chamber, driving a setting or drive piston for the fastening elements. Generally, with such setting tools, it is desirable to achieve the most possible thermal efficiency.
U.S. Pat. No. 4,403,722 discloses a combustion-engined setting tool with a combustion chamber for combusting a mixture of air and fuel gas and on a rear wall of which a ventilator is arranged. The ventilator is driven by an electric motor, providing a turbulent regime in the combustion chamber during operation of the ventilator, whereby the thermal efficiency is increased in comparison with combustion in a non-turbulent regime.
The drawback of the setting tool of the U.S. Pat. No. 4,403,722 consists in that the combustion in the combustion chamber occurs under the atmospheric pressure, so that peak pressures achieved during combustion usually lie within a range between 5-6 bar. Therefore, the efficiency with reference to the calorific value of the combusted fuel is smaller than 10%.
U.S. Pat. No. 4,415,110 discloses a hand-held setting tool that includes a piston displaceable in a first cylinder and which is connected with a setting piston displaceable in a second cylinder by a gear drive. In the initial position, the piston in the first cylinder is located in the vicinity of a spark plug, whereas the setting piston in the second cylinder is located in an opposite end region remote from the spark plug in the second cylinder. When the setting tool is pressed with a movable arm against a constructional component, the spark plug in the first cylinder ignites the gas-air mixture therein. As a result, the piston in the first cylinder moves away from the spark plug, whereby the gear drive displaces the setting piston in the second cylinder toward the spark plug therein, compressing the gas-air mixture in the second cylinder. Then, the gas-air mixture in the second cylinder is also ignited by the spark plug therein, with the setting piston being accelerated in a direction away from the spark plug in the second cylinder, driving, with its stem, a fastening element into the constructional component. The combustion pressure is increased due to the pre-compression of the gas-air mixture.
The drawback of the setting tool of U.S. Pat. No. 4,415,110 consists in that the stem of the setting piston, in its initial position at the end region of the second cylinder remote from the spark plug, is located in the nail guide, blocking feeding of a new nail. Therefore, little time is available for feeding a new nail in the nail guide when the setting piston is located in the region of the second cylinder adjacent to the spark plug therein. This is critical when longer nails are being driven in, and it can lead to malfunction of the setting tool.
Accordingly, an object of the present invention is to provide a setting tool in which the drawbacks of the known setting tools are eliminated, and a high thermal efficiency is achieved.